Accomodation: Focusing within the eye to increase the optical power to maintain a clear image as an object is moved closer. This is accomplished by the natural lens of the eye changing its shape (both contracting to focus up close and then relaxing to focus on more distant objects). A combination of ciliary muscle contraction and the zonular relaxation facilitates this change in shape.

Accomodative Insufficiency: Reduced focusing power (accommodation) related to age. This typically happens at age 40 or over and is called presbyopia.

Accomodative Spasm: A muscle spasm of the natural lens of the eye in which the lens does not relax after accommodating. This results in vision that is sharp for near but blurry for distance. This condition can be helped with Dr. Mandel’s computer tips.

Amblyopia (AKA: “lazy eye”): Decreased vision in one or both eyes when the eye(s) are otherwise physically normal. This can be due to muscle alignment problems called strabismus or different prescriptions in the eyes, which is called anisometropia. This condition can usually be improved with patch therapy, but only if this is initiated prior to age 5. The earlier the intervention, the better the prognosis will be.

Anterior Chamber: The space within the eye between the innermost layer of the cornea (endothelium) and the iris. This space is filled with a fluid known as aqueous humor. An open angle is necessary to drain the normal fluid within the eye. If the angle closes, it can lead to narrow angle glaucoma, which is an ophthalmic emergency when acute.

Applanation Tonometry: The measurement of intraocular pressure , given in millimeters of mercury, in which the amount of force required to flatten an area of the cornea, by contact, is documented. This is a routine screening test for glaucoma.

ARMD (Age Related Macular Degeneration): A condition of the eye which involves deterioration of the macula resulting in loss of central vision. There are two types of ARMD, “dry” in which treatments are limited, and “wet” in which abnormal blood vessels grow under the retina and leak fluid and blood. The “wet” type of ARMD can usually be treated with laser photocoagulation which seals the leaky blood vessels. Although treatable in some cases, the prognosis is often worse with the wet type.

Astigmatism: A condition of the eye in which the curvature of the cornea focuses light rays at two different spots within the eye. This can create eyestrain and in some cases, blurry vision. This can be corrected with special toric contact lenses or spectacles, as well as with laser vision correction. Almost all people have some degree of astigmatism.

Avascular: Lack of blood vessels or blood supply.

Bandange Contact Lens: A soft contact lens that is used to cover and protect the epithelium of the cornea so that it is able to regenerate following trauma (eg: a corneal abrasion) or PRK refractive surgery.

Bifocal Lens: A special type of eyeglass lens that incorporates two different optical powers in the same lens, typically to correct both distance and near visual acuity.

Binocular: Referring to or affecting both eyes.

Binocular Vision: The blending of the separate images seen by each eye into one single image. Insufficient functioning of this process can lead to diplopia (double vision).

Blepharitis:Inflammation of the eyelids which can be accompanied by redness, swelling and itching of the eyes and/or lid margins. This condition can be caused by inflammation and/or infection and is often chronic. Treatment can include oralantibiotics as well as lid scrubs and hygiene and anti-inflammatory and antibiotic eye drops.

Blepharoplasty: A surgical procedure of the eyelids to remove redundant skin and fat. It is usually cosmetic, but in some cases it can affect vision.

Blepharospasm: Involuntary spasm of the muscle that controls the function of theeyelids which may lead to uncontrolled blinking and lid squeezing.

Cataract: An opacity or cloudiness of the crystalline lens of the eye. This can cause blurry vision as it can prevent a clear image from forming on the retina.Click here to watch a video about cataract surgery on our Mandel Vision YouTube channel.

Chalazion: An inflamed bump within the eyelid that is within a meibomian gland.

Ciliary Body: The tissue that lines the inside of the eye which is composed of the ciliary muscle and other ciliary processes. These ciliary processes produce aqueous.

Ciliary Muscle: The smooth muscle portion of the ciliary body which is responsible for the contraction and relaxation of zonules which allow the lens of the eye to focus (accommodate) for near visual acuity.

Collagen: Connective tissue protein which is the structural backbone of the sclera, cornea, as well as other fibrous tissues of the body.

Concave Eyeglass Lens: A lens that is thicker at the edges than in the center which causes light rays from an object to diverge. This causes light rays in a myopic eye to focus on the retina which brings a blurry image in focus. Nearsighted eyes focus their light rays in front of the retina.

Cone: A light sensitive retinal receptor, most numerous in the macular area, that provides sharp visual acuity and is responsible for color vision.

Conjunctiva: The transparent mucous membrane that covers the outer surface of the eyeball (sclera), but excludes the cornea. It also lines the inner surface of the eyelids.

Conjunctivitis (AKA: “pink eye”): Inflammation of the conjunctiva. This condition is usually characterized by discharge, grittiness, redness and swelling. It can be allergic, viral or bacterial and is typically treated with eyedrops.

Convergence Insufficiency: A weakening of the eye muscles responsible for pulling the eyes toward each other to maintain single vision during near vision fixation. This can cause eye fatigue as well as diplopia (double vision).

Collagen: Connective tissue protein which is the structural backbone of the sclera, cornea, as well as other fibrous tissues of the body.

Contact Lens: A small disc made of various silicone and or plastic materials usually containing an optical correction which is worn over the cornea as an alternative to spectacles.

Convex Eyeglass Lens: A lens that is thicker in the center than at the edges, which causes light rays from an object to converge. This causes light rays in a hyperopic (farsighted) eye to focus on the retina which brings a blurry image in focus. Farsighted eyes usually focus their light rays behind the retina.

Corneal Pannus: Infiltration of the cornea by abnormal blood vessels in an otherwise avascular tissue. This is typically the body’s defensive response to a lack of oxygen to the cornea which can be caused by an improper fitting contact lens and/or sleeping in contact lenses.

Corneal Transplant: A surgical procedure, performed by a corneal specialist, in which a scarred or diseased cornea is replaced with clear corneal tissue from a human donor.

Corneal Ulcer: A discontinuity or break in the epithelial tissue of the cornea associated with inflammation in the cornea, that could be sterile or may be caused by bacterial, fungal or viral infection. This is commonly seen in patients who over wear and/or sleep in their contact lenses and requires immediate treatment because it can be vision threatening, especially if it is located in the area of central vision.

Crystalline Lens: The natural lens of the eye. Comprised of transparent intraocular tissue, it helps bring rays of light to a focus on the retina.

Cylindrical Eyeglass Lens: A lens that produces a different refractive power in each meridian which is used for correcting astigmatism.

Depth Perception: Awareness of the relative spatial location of objects; some being closer to the observer than others. This can be binocular or monocular.

Descemet’s Membrane: Thin layer deep within the cornea. The tissue of this membrane is just behind the endothelium and composed of collagen and elastic threadlike fibers.

Detachment: Separation of tissues from their normal anatomical attachments.

Diabetes Mellitus: A condition in which the pancreas no longer produces enough insulin or cells stop responding to the insulin that is produced, so that glucose in the blood cannot be absorbed normally into the cells of the body. This is usually a chronic disease that can cause serious health complications including renal (kidney) failure, heart disease, stroke, and blindness.

Dilation (Pupillary): The widening of the pupil induced by eye drops to facilitate an examination of the fundus, the posterior portion of the eye, which includes: the retina, optic nerve and disc, macula and blood vessels.

Diopter: The unit of measure used in ophthalmology to designate the refractive power of a lens.

Diplopia (AKA: double vision): The perception of two images from one object. These 2 images can be vertical, horizontal or diagonal from each other. It occurs only with two eyes together and disappears when one eye is covered.

Direct Ophthalmoscope: A handheld device used to visualize the fundus (retina) of the eye. It provides a magnified upright image of the retina.

Divergence: The spreading apart of light rays as they leave an object or when they are refracted through a minus power lens.

Dominant Eye: The preferred eye for visual tasks. This is also the eye that leads and controls the other eye during binocular eye movements.

Dua’s Layer: One of the 6 layers of the cornea. Previously undetected, the discovery of this layer was published by scientists at The University of Nottingham in 2013 after several years of research. This layer is situated between the stroma and Descemet’s membrane. Although this layer is thin, (only one hundredth the thickness of the entire cornea) it is a very strong layer.

Ectasia: In ophthalmology this term can mean a weakening of the cornea.

Ectropion: A turning out of the eyelid; usually the lower lid.

Edema: Swelling of tissues due to excess fluid accumulation.

Emmetropia: Absence of refractive error. Images of objects are focused sharply on the retina without the need for corrective lenses.

Endothelium: The innermost surface of the cornea, situated between Descemet’s membrane and the anterior chamber. It acts as a pump to keep excess water out of the stroma. The cornea needs to be more dehydrated than the rest of the body in order for it to be a clear window in the front of the eye.

Epidemic Kerato-Conjunctivitis (EKC): Highly contagious viral infection of the cornea and conjunctiva which is caused by an adenovirus.

Episcleritis: Inflammation of the episclera, the outermost layer of the sclera. Symptoms include pain and photophobia. Signs include redness. Most cases are of unknown etiology (cause).

Epithelium: The outermost layer of the cornea, situated between Bowman’s membrane and the tear film. This is the part of corneal tissue that is removed with the excimer laser during laser vision correction.

Eye (Eyeball, Globe): A sensory organ for sight which is composed of three major structural layers (corneo-sclera, uvea and retina). The eye receives light imagery from objects and transmits this visual information to the brain.

Flashes: Sensation of light often a result of the tugging of the vitreous away from the retina. It can also be caused by a newly formed retinal tear, retinal detachment or a form of migraine. This symptom should be evaluated by an ophthalmologist as quickly as possible to rule out a retinal hole or retinal tear which may be repaired by laser or surgically.

Floaters: Particles that float in the vitreous (jelly that fills the eye) and cast shadows on the retina causing visual symptoms. These particles are usually seen as spots or cobwebs.

Fovea: The central point of the macula that produces the sharpest vision.

Hypertensive Retinopathy: Changes in the retina that may be caused by hypertension (high blood pressure).

Indirect Ophthalmoscope: Instrument consisting of a bright light source and a handheld magnifying lens used to visualize the posterior portion of the eye (the fundus). It creates an inverted image of the fundus projected in the front of the eye. This instrument has a wider field of view than the direct ophthalmoscope and the binocular model allows stereoscopic depth perception of the retina.

Intraocular: Inside the eye.

Intraocular Lens (IOL): A plastic lens that is surgically implanted to replace the natural lens of the eye. The lenses are available in various optical powers that can correct myopia and hyperopia. This is done routinely during cataract surgery and is also implanted during clear lens extraction, a form of intraocular refractive surgery.

Intraocular Pressure: Fluid pressure within the eye.

Iris: The pigmented tissue behind the cornea which gives color to the eye and controls the amount of light entering the eye by changing the size of the pupillary opening. This function of the iris is similar to the aperture of a camera lens.

Iritis: Inflammation of the iris that can cause pain, tearing, blurred vision, small pupil and redness, but can also be painless.

Irregular Astigmatism: A type of astigmatism producing distorted imagery in which the light rays are not oriented 90 degrees apart. It may be due to contact lens wear, trauma, inflammation as well as developmental abnormalities.

Keratoconus: A degenerative corneal disease which may affect vision and is characterized by thinning and cone-shaped protrusion of the central cornea. This disease typically affects both eyes, although not symmetrically, and usually becomes apparent in the 2nd decade of life.

Keratitis Sicca: (AKA: Dry Eyes): A condition of the eye which involves both corneal and conjunctival dryness due to deficient tear production. Symptoms include foreign body sensation, redness and burning.

LASIK (Laser In-Situ Keratomileusis): LASIK is a laser vision correction procedure that combines a flap created by a microkeratome or an intralase laser, along with an excimer laser to correct visual refractive abnormalities. It combined two previously used surgical procedures (listed below) and has been performed millions of times worldwide:

1. The creation of a corneal flap by a procedure known as keratomileusis.
2. The use of an excimer laser to precisely reshape the corneal tissue beneath the flap. This enables light rays to be more accurately focused on the retina at the back of the eye, thereby improving vision. The flap is then returned to its original position.

Narrow Angle Glaucoma: A form of glaucoma which is categorized by a rise in intraocular pressure in patients with narrow anterior chamber angles. This condition can be acute with accompanying pain and loss of vision if not treated promptly.

Nasolacrimal Duct: Tear drainage channel that connects the lacrimal sac to an opening in the mucous membrane in the nose.

Ocular Migraines (AKA: Ophthalmic Migraines): A disorder in which spasm and then dilation of blood vessels, or unusual electrical brain activity, causes a temporary change of vision the eye. Symptoms can include lightening flashes, expanding circles of light and temporary vision loss.

Ocular Motility: The movement of the eyes which involves the extraocular muscles and their effect on eye movement.

Open Angle Glaucoma: The most common type of glaucoma in which the anterior chamber is open. It is characterized by an increase in intraocular pressure which causes damage to the optic nerve as well as visual field (peripheral vision) loss. There are types of open angle glaucoma called low tension, or low pressure, glaucoma that do not have an increased level of pressure but do damage to the eye. Open angle glaucoma is painless and that is why regular eye exams are so important. Vision may not be affected until it is too late to treat. Click here to watch a video about open angle glaucoma on our Mandel Vision YouTube channel.

Ophthalmic Technician: An allied health professional (both certified and non-certified) who performs preliminary diagnostic testing for an ophthalmologist.

Ophthalmologist: A surgeon (M.D.) who specializes in diagnosis and treatment ofrefractive, medical and surgical problems related to eye diseases and disorders, as well as vision conditions with spectacles and contact lenses.

Ophthalmology: Medical specialty which deals with the eye, its function and diseases, including diagnosis and medical as well as surgical management of these diseases.

Optic Cup: A depression in the center of the optic disc located in the posterior part of the eye. The optic cup usually occupies one-third or less of the total disc diameter. It is evaluated as part of a glaucoma exam.

Optic Disc: The ocular end of the optic nerve. The retinal nerve fibers exit the eye and blood vessels enter the eye through the optic disc.

Optic Nerve: The second cranial nerve and the largest sensory nerve of the eye. The optic nerve carries impulses for sight from the retina to the brain’s visual cortex.

Optics: The branch of physics that deals with the properties of light and vision, for instance its refraction and reflection by lenses, prisms, mirrors and the eye. Two principal areas of optics that apply to ophthalmology are physical optics and geometric optics.

Orthokeratology (AKA: Ortho-K): A system of treating myopia and astigmatism with a sequential series of flatter-than-normal contact lenses that gradually flatten the cornea. In orthokeratology, patients wear the contact lenses while sleeping.

Orthophoria: Eyes that are aligned normally; the absence of an eye deviation (or eye turn).

Orthoptics: The science that deals with the diagnosis and treatment of defective eye coordination, binocular vision, strabismus and functional ambylopia by non-medical and non-surgical methods.

Patch Therapy: Treatment of amblyopia which involves occluding an ambyopic patient’s better seeing eye to improve vision in the amblyopic eye. This form of therapy is most effective when it is begun before age 8.

Perimetry: A method of charting the extent of a stationary eye’s visual field (peripheral vision) with test objects of various sizes and light intensities.

Peripheral Vision: Side vision. This vision is produced by light rays from an object falling on areas of the retina that are distant from the macula.

Pinhole device: An opaque disc with one or more holes which blocks all but the centermost light rays from an object. It is used as a quick screening device to determine whether reduced vision is caused by refractive error. (Vision through the pinhole will improve if the decreased vision is caused by refractive error.)

PRK (Photorefractive keratectomy):Refractive surgery performed with an excimer laser on the corneal surface after the epithelium is removed with the use of a gentle epithelial brush. The difference between this procedure and LASIK is that there is no flap created in PRK.

Progressive Eyeglass Lens (Invisible bifocals): An eyeglass lens that incorporates corrections for distance, middle and near vision without any visible bifocal line.

Punctal Occlusion: Blocking the punctum in the eyelids to prevent quick drainage of liquid from the eye to the nasolacrimal duct. When using eye drops, punctual occlusion is sometimes recommended so that eye drops stay on the eye longer. This is accomplished by closing the eye and pressing on the inner corner of the eye for 2 minutes after instilling drops. This can also be accomplished with the use of punctual plugs for the treatment of dry eye symptoms.

Punctal Plugs: Small silicone (permanent) or collagen (absorbable) inserts that are placed inside the punctum of the eyelids to prevent normal tear drainage. These plugs are used to treat dry eyes to keep natural tears on the eye longer to help the cornea and conjunctiva stay moist.

Punctum: Tiny skin opening of the upper and lower eyelids, near the nose. This is the entrance to the tear drainage system. (Plural: puncta.)

Pupil: Black circular opening in the center of the iris that changes size to regulate the amount of light entering the eye.

Pupillary Distance (P.D.): The distance between the pupillary centers of opposing eyes. This measurement is critical to making eyeglasses as the optical center of each lens needs to be centered over the pupil of each eye.

Pupillometer: An ophthalmic instrument used to measure the size (diameter) of the pupil.

Red Reflex: Normal red glow emerging from the pupil when the eye is illuminated. It is this reflex that is analyzed during retinoscopy to determine an eye’s refractive error objectively.

Refract: To bend. In ophthalmology, light rays are refracted when they pass through different types of lenses.

Refraction: A subjective determination of an eye’s refractive error as well as the best prescription for eyeglasses and contact lenses to correct it. This test involves a series of lenses in graded powers which are presented to the patient to determine which lens, or combination of lenses, provides the sharpest visual acuity.

Retina: Light sensitive nerve tissue in the eye, composed of rods and cones, that converts images from the eye’s optical system into electrical impulses that are sent along the optic nerve to the brain to be interpreted as vision.

Retinal Detachment: Separation of the retina from the underlying pigment epithelium. This causes decreased vision and often requires immediate surgical repair.

Retinoscope: A hand held instrument which is used to determine an eye’s refractive error objectively (with no response required from the patient). Light from the retinoscope is projected into the eye and the movements of the light reflection are neutralized (eliminated) with corrective lenses.

Retinoscopy: An objective measurement of an eye’s refractive error by using a retinoscope.

Rod: A light-sensitive, retinal receptor that works at low light levels which enables the eye to adapt to night vision conditions.

Sclera: Opaque, fibrous, protective outer layer of the eye. The sclera is seen as the ‘white’ part of the eye surrounding the ‘colored’ part of the eye and is covered by the conjunctiva. The sclera is continuous with the cornea in front and the sheath covering the optic nerve in the back of the eye.

Single Vision Eyeglass Lens: An eyeglass lens that corrects only one type of refractive error.

Slit-Lamp Biomicroscope: A table-top microscope that is used to examine the anterior portion (front portion) of the eye. This instrument cross-sections the eye so that the structures of the eye can be viewed in layer-by-layer detail. With the aid of a special handheld lens, it can also be used to examine the posterior portion (back portion or fundus) of the eye.

Soft Contact Lens: A hydrophilic (water-absorbing) contact lens that rests on the cornea and is used for correcting a refractive error or protecting a damaged corneal surface.

Snellen Chart: A test chart for assessing visual acuity. The chart contains rows of letters, numbers or symbols in standardized sizes with a designated distance at which each row should be legible to the normal eye. The standard testing distance is typically 20 feet.

Specular Endothelial Microscopy: A diagnostic test which allows the examiner to visualize both the pattern and density of endothelial cells through magnification via a technique that uses a slit lamp microscope in combination with light reflection from the endothelium.

Spherical Aberration: Type of visual aberration caused by light rays from an object hitting the periphery of the eye (cornea and crystalline lens) instead of the center of vision. This can cause the light rays to be over-refracted (bent too much) which causes blurred vision (positive spherical aberration). Click here to learn more about spherical aberration, as well as Dr. Mandel’s personalized approach to laser vision correction in our blog: The Customization of Laser Vision Correction.

Strabismus (Deviation): Eye misalignment or eyes that do not move normally, caused by extraocular muscle imbalance. This imbalance causes the foveas of opposite eyes to be focused on different objects. This can cause eyestrain as well as diplopia.

Stroma: The middle layer tissue that forms 90% of the cornea. It is situated beneath Bowman’s membrane and above Descemet’s membrane and is composed of layered collagen fibers and cells. It is this layer of the cornea that is mainly reshaped during laser vision correction.

Stye: An acute infection of the oil glands of Zeis, located in an eyelash follicle at the eyelid margin. The symptoms include tenderness to touch and presents as an inflamed red bump.

Subconjunctival Hemorrhage: Bleeding from a small blood vessel under the conjunctiva. It presents as bright red blood over the sclera and can be spontaneous of unknown cause or be caused by coughing or straining, for instance when lifting heavy weight. It usually resolves on its own in a week or two, without treatment.

Tear Break-Up Time (BUT): A test for tear film function, this is the interval between a blink and the development of a dry spot in the pre-corneal tear film. This test is performed using flourescein eye drops in combination with the ultraviolet filter in a slit-lamp biomicroscope. A lower BUT may indicate dryness.

Ultrasound: A method of diagnostic testing in which high frequency sound waves are transmitted into the eye from a hand-held probe. The sound waves are reflected by the ocular tissues. This method is used in pachymetry to measure the thickness of the cornea, in Ascan biometry to measure the length of the eye and in Bscan biometry to aid in the diagnosis of eye and orbital problems.

Visual Acuity: Assessment of the eye’s ability to distinguish object details and shape, using the smallest object that can be seen at a specified distance, typically at 20 feet. Click here to watch a video about the visual system on our Mandel Vision YouTube channel.

Visual Field: The full area of both central and peripheral vision that is visible to an eye that is fixating straight ahead. Also the name of a diagnostic instrument used to measure peripheral vision.

Vitreous: The transparent, gel-like mass which fills the back two-thirds of the eyeball, between the crystalline lens and the retina and gives the eyeball its shape.